On the interpretation and use of neutron calibration coefficients

Calibration laboratories provide measurement services that include determining the calibration coefficients for neutron survey meters and personal dosemeters. While there are numerous documents dealing with the procedures for calibration of neutron measuring devices, the purpose of this paper is to clarify the use of the particular dose equivalent conversion coefficients used at the National Institute of Standards and Technology and the Pacific Northwest National Laboratory for these calibrations.

The incidence of work-related disease reported by occupational physicians, 1996-2001

In the course of six calendar years, 1996-2001, 5491 new cases of work-related disease were reported by a 1-in-12 random sample of occupational physicians throughout the UK. This represented an estimated total of almost 66 000, or 11 000 cases per annum. These cases have now been analysed by sex, occupation (nine categories) and industry (eight categories), and annual average incidence rates calculated in five main disease groups against a similarly classified denominator of 3.2 million employees served by the same physicians. The overall average annual estimated rate (342 per million) was eight times higher than that reported by clinical specialists, calculated in a similar manner against the entire employed population of the UK (28 million), but 17 times higher for musculoskeletal disease. For men employed in mines and quarries, and both men and women in metallic and automotive manufacture, rates for most types of disease were very high. Occupations with the highest rates were craftsmen and female associate professionals. In all these occupational and industrial groups with high rates, musculoskeletal complaints were the main cause, and skin, respiratory or stress diseases were next in importance. In each type of disease, there was a wide range in incidence rates, suggesting important differences in risk by occupation or industry.

The estimated workforce served by occupational physicians in the UK

During the past decade, an occupational disease surveillance scheme has been created in the UK, based on systematic reporting of newly diagnosed cases by six groups of clinical consultants and by specialist occupational physicians. Labour Force Survey statistics have proved a reasonably satisfactory denominator for the former, but not for the occupational physicians, who provide services for only a selected subsection of the employed population. To remedy this deficiency, approximately 700 occupational physicians who were recorded as having been a reporter at some time were invited to provide their best estimate of the number of employees for whom they were responsible. After various exclusions--mainly physicians who were not, or were no longer, responsible for any defined workforce, and others who had not reported for at least 3 years--the number of active participants for whom data, by industry, occupation and sex, were obtained or estimated was 503. The resulting total number of employees served was estimated at 3.2 million, comprising 12% of the general working population. The proportion with access to an occupational physician varied enormously, from 43% in the health and social services to 1% in agriculture, forestry and fishing, and 6% in the rest of industry. Numbers estimated for each industrial sector were fairly reliable, but by occupation less so, especially in the health and social services.

Soluble HLA-II expression in African-Americans

OBJECTIVE

In this study we evaluated the contribution of major histocompatibility complex (MHC) genes to soluble histocompatibility antigen class II (sHLA-II) secretion in African American patients with rheumatoid arthritis (RA).

METHODS

A sensitive enzyme-linked immunoassay was used to quantitate sHLA-II in the serum of 7 patients with RA, as well as 28 of their kinships and 49 HLA typed normal African American individuals.

RESULTS

Mean sHLA-II values were higher in patients with RA than those in healthy African American individuals (p < 0.05). There were variations in concentrations in individual patients but these were unrelated to any apparent clinical event. The proportion of unaffected family members with detectable levels of sHLA-II was not significantly different than those in normal controls. Neither specific HLA-haplotype, or HLA-allele(s) correlated with high or low sHLA-II secretion.

CONCLUSIONS

Our data suggest that sHLA-II molecules are not regulated by MHC linked genes but may be regulated by non-MHC linked genes and racial background may reflect genetic heterogeneity of the expression of this soluble HLA material. These observations contrast with previous observations concerning soluble HLA class I (sHLA-I) molecules in a described population sample which were almost the precise reverse.

Surveillance for work-related hearing loss in the UK: OSSA and OPRA 1997-2000

Surveillance data on occupational audiological disorders have been collected by the Occupational Surveillance Scheme for Audiological Physicians (OSSA) since October 1997 and by the Occupational Physicians Reporting Activity (OPRA) from January 1996. During the 3 years ending in September 2000, a total of 1620 new cases were received from consultant audiological physicians; 988 new cases were estimated from reports by occupational physicians in the period from October 1997 to September 2000. The annual incidence of occupational noise-induced hearing loss (NIHL) was 1.94 and 1.23 per 100 000 workers for the OSSA and OPRA schemes, respectively. The median age at diagnosis with NIHL was 59 years in OSSA reports and 50 years in OPRA; nearly all cases were seen in men (95.6 and 92.5% male cases for OSSA and OPRA, respectively). High incidence rates based on OSSA reports were seen in foundry labourers (64.0 per 100 000 employed), coal gas and coke oven furnace workers (54.6), workers in transport and communication (43.1), metal workers (31.3), and members of the armed forces (28.3). Data from occupational physicians point to high rates in sawyers and woodworking machinists, metal furnace workers, coach and carriage builders, maintenance fitters, and engineering labourers. Among workers aged < or =45 years, those in manufacturing and the armed forces were prominent. The long latency of occupational hearing loss makes surveillance difficult, but consistent patterns in occupational risk suggest targets for preventive efforts.

Microdosimetric properties of ionizing electrons in water: a test of the PENELOPE code system

The ability to simulate the tortuous path of very low-energy electrons in condensed matter is important for a variety of applications in radiobiology. Event-by-event Monte Carlo codes such as OREC, MOCA and PITS represent the preferred method of computing distributions of microdosimetric quantities. However, event-by-event Monte Carlo is computationally expensive, and the cross sections needed to transport simulations to this level of detail are usually only available for water. In the recently developed PENELOPE code system, 'hard' electron and positron interactions are simulated in a detailed way while soft' interactions are treated using multiple scattering theory. Using this mixed simulation algorithm, electrons and positrons can be transported down to energies as low as 100 eV. To our knowledge, PENELOPE is the first widely available, general purpose Monte Carlo code system capable of transporting electrons and positrons in arbitrary media down to such low energies. The ability to transport electrons and positrons to such low energies opens up the possibility of using a general purpose Monte Carlo code system for microdosimetry. This paper presents the results of a code intercomparison study designed to test the applicability of the PENELOPE code system for microdosimetry applications. For sites comparable in size to a mammalian cell or cell nucleus, single-event distributions, site-hit probabilities and the frequency-mean specific energy per event are in reasonable agreement with those predicted using event-by-event Monte Carlo. Site-hit probabilities and the mean specific energy per event can be estimated to within about 1-10% of those predicted using event-by-event Monte Carlo. However, for some combinations of site size and source-target geometry, site-hit probabilities and the mean specific energy per event may only agree to within 25-60%. The most problematic source-target geometry is one in which the emitted electrons are very close to the tally site (e.g., a point source on the surface of a cell). Although event-by-event Monte Carlo will continue to be the method of choice for microdosimetry, PENELOPE is a useful, computationally efficient tool for some classes of microdosimetry problem. PENELOPE may prove particularly useful for applications that involve radiation transport through materials other than water or for applications that are too computationally intensive for event-by-event Monte Carlo, such as in vivo microdosimetry of spatially complex distributions of radioisotopes inside the human body.

Highly active antiretroviral therapy-associated regression of cytomegalovirus retinitis: long-Term results in a small case series

PURPOSE

To report the stability of acquired immunodeficiency syndrome (AIDS)-associated cytomegalovirus (CMV) retinitis lesions that have undergone regression in the absence of specific anti-CMV medications owing to highly active antiretroviral therapy (HAART)-generated immune recovery.

METHODS

The initial examination revealed HAART-associated regression of CMV retinitis lesions in eight subjects at two institutions. Patients were monitored for recurrences of CMV activity. CD4+ T-lymphocyte counts and human immunodeficiency virus (HIV) loads were measured.

RESULTS

All patients had positive initial responses to HAART with an average HIV load decrease of 2.26 log units (range 0.3-5.57). Mean CD4+ T-lymphocyte count at baseline was 45.6 (range 4-107) and increased by an average of 132.5 (range 7-266) within the first 2 to 4 months of HAART. Patients were observed for an average of 15.5 months (range 11-20 months). Six subjects had a vigorous and sustained response to therapy, achieving an average HIV load of 9,400 copies/mL (3.32 log10 decrease) and CD4+ T-lymphocyte count of 158.2 cells/microL. These patients had no CMV retinitis progression. By contrast, two others who attained an average log10 decrease of only 0.48 had modest and short-lived increases in the CD4+ T-lymphocyte count. These patients experienced reactivation of CMV retinitis after 5 and 7 months, respectively.

CONCLUSIONS

Regressed CMV retinitis may remain healed for long periods. However, failure of HAART to induce substantial decreases in HIV load may predict poor or unsustainable rises in the CD4+ T-lymphocyte count and presage recurrence of CMV retinitis. Vigilance in ophthalmic examinations is especially mandatory in these subjects.

Spectral emissions and dosimetry of metal tritide particulates

Inference of intakes and doses from inhalation of metal tritide particles has come under scrutiny because of decommissioning and decontamination of US Department of Energy facilities. Since self-absorption of radiation is very significant for larger particles, interpretation of counting results of metal tritide particles by liquid scintillation requires information about emission spectra. Similarly, inference of dose requires knowledge of charged particle and photon spectra. The PENELOPE Monte Carlo radiation transport computer code was used to compute spectral emissions and other dosimetric quantities for tritide particulates of Sc, Ti, Zr, Er, and Hf. Emission fractions, radial absorbed dose distributions, specific energy distributions and related frequency-mean specific energies and lineal energies, and the emitted spectra of electrons and bremsstrahlung photons are presented for selected particulates with diameters ranging from about 0.01 microm to 25 microm. Results characterising the effects of uncertainties associated with the composition and density of the tritides are also presented. Emission spectra are used to illustrate trends in the relationship between apparent and observed activity as a function of particle type and size. Emissions from metal tritide particles are weakly penetrating, and electron emission spectra tend to 'harden' as particle size increases. Microdosimetric considerations suggest that the radiation emitted by metal tritides can be classified as a low linear energy transfer radiation source. For cells less than about 7 microm away from the surface of a metal tritide, the primary dose component is due to electrons. However, bremsstrahlung radiation may deposit some energy tens, hundreds or even thousands of micrometres away from the surface of a tritide particle. The data and analyses presented in this report will help improve the accuracy of dose determinations for particulates of five metal tritides. Future work on the spectral emissions and dosimetry of metal tritide particulates needs to consider the contributions of so-called internal bremsstrahlung, an additional form of bremsstrahlung radiation emitted during beta decay.

Current challenges in personal dosimetry at the US DOE Hanford site

An overview is presented of the dosimetry system, dose equivalent calculation methodology, and QA/QC practices used at the US Department of Energy Hanford site. It describes some of the problems encountered in accurately measuring dose equivalent quantities under a broad range of field conditions that do not necessarily correlate with laboratory calibration conditions and the approach taken to solve these problems. Personnel at Hanford are monitored with a combination of Harshaw model 8825 and 8816 thermoluminescence dosemeters and CR-39 etched track dosemeters. Extremities are monitored using the ICN MeasuRing loaded with a Harshaw XD740 chipstrate TLD. All dosemeters employ LiF:Mg,Ti elements that are read on-site with Harshaw model 8800 and 6600 TLD readers. CR-39 dosemeters are electrochemically etched in non-commercial etch chambers and counted with an automated track counting system developed by Pacific Northwest National Laboratory. Problems with over response of the 8825 with respect to Hp(0.07), under-response of the 8825 with respect to Hp(3), and over response of the 8825 with respect to Hp(10) in Hanford's 90Sr/90Y beta radiation fields are discussed. Approaches to measurement of the operational quantities for field conditions and algorithm solutions to the above problems are described. Methods used to calibrate the ring dosemeter for Hanford field conditions together with limitations of the ring dosemeter in measuring Hp(0.07) for extremities, particularly when covered with protective clothing, are also discussed.

Fabrication of a configurable, single-use microfluidic device

This paper describes microfluidic devices that contain connections that can be opened by the user after fabrication. The devices are fabricated in poly(dimethylsiloxane) (PDMS) and comprise disconnected fluidic channels that are separated by 20 microm of PDMS. Applying voltages above the breakdown voltage of PDMS (21 V/microm) opened pathways between disconnected channels. Fluids could then be pumped through the openings. The voltage used and the ionic strength of the buffer in the channels determined the size of the opening. Opening connections in a specific order provides the means to control complex reactions on the device. A device for ELISA was fabricated to demonstrate the ability to store and deliver fluids on demand.

Case-referent survey of young adults with mesothelioma: I. Lung fibre analyses

OBJECTIVES

Our study aimed to determine the lung tissue concentration of asbestos and other mineral fibres by type and length in persons with mesothelioma aged 50 yr or less at time of diagnosis, compared to controls of similar age and geographical region. In this age group it was thought that most, but not all, work-related exposures would have been since 1970, when the importation of crocidolite, but not amosite, was virtually eliminated.

METHODS

Eligible cases were sought from recent reports by chest physicians to the SWORD occupational disease surveillance scheme. Lung tissue samples were obtained at autopsy from 69 male and four female cases, and mineral fibres identified, sized and counted by electron microscopy. Fibre concentrations per microg dry tissue were compared with similar estimates from a control series of autopsies of sudden or accidental deaths. Unadjusted, and adjusted odds ratios calculated by logistic regression, assessed relative risk in relation to fibre type, length and concentration.

RESULTS

Unadjusted and adjusted odds ratios increased steadily with concentration of crocidolite, amosite, tremolite and all amphiboles combined. There was also some increase with chrysotile, but well short of statistical significance. Incremental risk examined in a linear model was as highly significant for all amphiboles together as individually. Short, medium and long amphibole fibres were all associated with increased risk in relation to length. Mullite and iron fibres were significant predictors of mesothelioma when considered without adjustment for confounding by amphiboles, but, after adjustment, were weak and far from statistically significant.

CONCLUSIONS

In this young age group, amosite and crocidolite fibres could account for about 80% of cases of mesothelioma, and tremolite for some 7%. The contribution of chrysotile, because of low biopersistence, cannot be reliably assessed at autopsy, but to the extent that tremolite is a valid marker, our results suggest that it was small. The steep linear trend in odds ratio shown by amphiboles combined indicates that their effects may be additive, with increased risk from the lowest detectable fibre level. Non-asbestos mineral fibres probably made no contribution to this disease. Contrary to expectation, however, some 90% of cases were in men who had started work before 1970; this was so whether or not amosite or crocidolite was found in lung tissue.

Case-referent survey of young adults with mesothelioma: II. Occupational analyses

OBJECTIVES

Our study aimed to identify occupations at increased risk of developing mesothelioma in persons aged 50 yr or less, and to relate these occupations to lung tissue concentration of asbestos fibres by type. In this age group it was thought that most, but not all, work-related exposures would have been since 1970, when the importation of crocidolite, but not amosite, was virtually eliminated.

METHODS

Eligible cases were sought from recent reports by chest physicians to the SWORD occupational disease surveillance scheme. Work histories were obtained for 115 men and 13 women, usually with the help of the chest physicians or coroners. Jobs were coded by the Office of National Statistics, so that the observed years spent in each occupation could be compared with expected values from census data, 1960-90. Lung tissue samples were obtained at autopsy from 69 male and four female cases, and mineral fibres identified, sized and counted by electron microscopy.

RESULTS

Of 37 industrial occupations analysed, odds ratios were significantly raised in eight: five in the construction industry and the others in shipbuilding, the manufacture of cement products and the manufacture of non-metallic mineral products (including asbestos). The concentrations in lung of crocidolite and amosite fibres, which together could account for 80-90% of cases, did not differ between occupational categories; those for amosite were appreciably higher than for crocidolite. Tremolite fibres were rarely found.

CONCLUSION

Mesothelioma in this young age group is dominated by carpenters, plumbers, electricians and insulators in the construction industry, and is mainly attributable to amphibole exposure. Work in shipbuilding and manufacture of mineral products was less important than in earlier studies. Contrary to expectation, however, some 90% of cases were in men who had started work before 1970.

The reported incidence of work-related musculoskeletal disease in the UK: MOSS 1997-2000

Consultant rheumatologists participate in surveillance of work-related musculoskeletal conditions under the Musculoskeletal Occupational Surveillance Scheme (MOSS), which has been in operation since 1997. During the first 3 years of the scheme, an estimated total of 8070 cases and 8442 diagnoses were obtained, an average of slightly less than 2700 estimated cases each year. Disorders of the upper limb accounted for approximately 66% (5502) of the total, with hand/wrist/arm conditions (3693 cases) comprising the majority of these. Conditions of the lumbar spine and trunk (13% of cases), the cervical spine (12%) and the shoulder (12%) were also frequently reported. Pain with ill-defined pathology was reported in 35% of cases with hand and forearm disorders. Overall, 82% of cases were related to repetitive rather than single injury. The largest numbers of cases were seen in workers in craft occupations (1659) and in clerical and secretarial workers (1524). High rates of musculoskeletal conditions, particularly of upper limb disorders, are notable in mining. In most occupations, and overall, women were at greater risk than men.

An integrated fluorescence detection system in poly(dimethylsiloxane) for microfluidic applications

This paper describes a prototype of an integrated fluorescence detection system that uses a microavalanche photodiode (microAPD) as the photodetector for microfluidic devices fabricated in poly(dimethylsiloxane) (PDMS). The prototype device consisted of a reusable detection system and a disposable microfluidic system that was fabricated using rapid prototyping. The first step of the procedure was the fabrication of microfluidic channels in PDMS and the encapsulation of a multimode optical fiber (100-microm core diameter) in the PDMS; the tip of the fiber was placed next to the side wall of one of the channels. The optical fiber was used to couple light into the microchannel for the excitation of fluorescent analytes. The photodetector, a prototype solid-state microAPD array, was embedded in a thick slab (1 cm) of PDMS. A thin (80 microm) colored polycarbonate filter was placed on the top of the embedded microAPD to absorb scattered excitation light before it reached the detector. The microAPD was placed below the microchannel and orthogonal to the axis of the optical fiber. The close proximity (approximately 200 microm) of the microAPD to the microchannel made it unnecessary to incorporate transfer optics; the pixel size of the microAPD (30 microm) matched the dimensions of the channels (50 microm). A blue light-emitting diode was used for fluorescence excitation. The microAPD was operated in Geiger mode to detect the fluorescence. The detection limit of the prototype (approximately 25 nM) was determined by finding the minimum detectable concentration of a solution of fluorescein. The device was used to detect the separation of a mixture of proteins and small molecules by capillary electrophoresis; the separation illustrated the suitability of this integrated fluorescence detection system for bioanalytical applications.

Basicity of the amino groups of the aminoglycoside amikacin using capillary electrophoresis and coupled CE-MS-MS techniques

This paper describes the use of capillary electrophoresis (CE), and coupled CE and mass spectrometric techniques, to measure the values of the pKa of the amino groups of the aminoglycoside antibiotic amikacin and of its acetylated derivatives. These values of pKa (8.4, 6.7, 9.7, 8.4) were determined by measuring the electrophoretic mobilities of the molecules as a function of pH; they are within 0.7 unit of certain values reported in the literature (by 13C and 15N NMR spectroscopies) but resolved ambiguities left by these earlier studies. The range of values of pKa of amino groups also indicates the complex dependence of the acidity of a functional group (and thus the extent of ionization at a specified value of pH) on the molecular environment of that group.

Cohort mortality study of North American industrial sand workers. I. Mortality from lung cancer, silicosis and other causes

BACKGROUND

In 1997 a Working Group of the International Agency for Research on Cancer changed an earlier classification of crystalline silica as a human carcinogen from Group 2A to Group 1, though commenting that the carcinogenicity might vary with industrial circumstances and depend on additional factors affecting biological activity, including the distribution of its polymorphs.

OBJECTIVE

We aimed to determine whether pure quartz exposure uncomplicated by the presence of other contaminating carcinogens, as experienced by workers in the production of high-grade industrial sand, was causally related to an increased risk of lung cancer.

METHODS

A cohort of 2670 men employed before 1980 for 3 years or more in one of nine North American sand-producing plants and a large associated office complex was selected for study. Of the cohort, 2644 (99%) were traced through 1994, and certificated cause of death ascertained for 1025 (99%) of the 1039 men known to have died. Standardised mortality ratios (SMRs) were calculated for the main causes of death, using both US and state or provincial male mortality rates for reference.

FINDINGS

The main analyses of deaths, 20 or more years after first employment against regional rates, gave the following SMRs: all causes 109, lung cancer 139, other malignancies 98, non-malignant respiratory disease 161, and nephritis/nephrosis 244. There were, in total, 37 deaths from silicosis or silico-tuberculosis, with one or more death at least in all nine production plants. Analyses failed to show any relation between lung cancer risk and duration of employment. The increased SMR for lung cancer was wholly due to high rates in four plants in two states, whereas no increase was found in the remainder of the cohort.

CONCLUSION

In the absence of information on smoking histories and risk in relation to estimated exposure, the increased SMR for lung cancer (139), although statistically significant, cannot be attributed confidently to crystalline silica. An answer to the question of attributability must await the findings of the nested case-control study, in which level of exposure and smoking habits were ascertained for cases and matched controls. The strong indication in this cohort of excess mortality from non-malignant renal disease deserves further investigation.

Diverticulitis in the young patient

Although predominantly a disease in older adults diverticulitis does affect younger patients. The disease has been described as not only rare but virulent by some authors, and a young patient age is considered to be a relative indication for early sugery. The goal of this study was to evaluate the experience of the Louisiana State University Health Sciences Center-Shreveport and affiliated hospitals with diverticulitis in young patients. This study was a retrospective chart review of 22 patients with diverticulitis age 40 years and younger over the past 20 years. Inclusion criteria were either a diagnosis of diverticulitis confirmed at surgery or positive CT findings and/or a positive contrast enema. The mean age in this study was 32.1 years (range 16-40). All 22 patients presented with abdominal pain. The next most common symptom was nausea and/or vomiting in 45 per cent followed by fever and chills in 36 per cent. Twelve patients had abdominal CTs on admission, and 87 per cent had positive findings. Eighteen patients underwent an operation. Four patients were treated nonoperatively. Nineteen patients had diverticulitis of the sigmoid colon. The remaining three had right-sided diverticulitis. Two patients underwent right hemicolectomy, and one underwent cecectomy. Of the 15 patients with sigmoid diverticulitis 12 (80%) underwent a two-stage procedure of sigmoid colectomy, end colostomy, and Hartmann's pouch. Three patients (20%) underwent a one-stage procedure of sigmoid colectomy and primary anastomosis. Two of three patients undergoing a one-stage procedure required reoperation. Postoperative complications occurred in 10 of 18 patients for an overall incidence of 56 per cent. Two of these patients had septic complications. Both of these patients had a delay in time from admission until operation: one for 7 days and the other for 10 days. There was one death in the series. Colostomy closure was performed successfully in nine of 12 (75%) patients. The mean time interval before closure was 7.7 months, (range 3-14). Patients with two-stage procedures on initial admission fared better than those with one-stage procedures. The overall mortality was 4.5 per cent. There was a high overall complication rate of 56 per cent in patients undergoing an operation. Two patients who had a delay in time from admission to operation had septic complications. Early surgical intervention should be considered in this clinical setting. In summary, although rare, diverticulitis in the young patient is often a fulminant illness requiring operation early in the disease process.